A transistor with a parallel tuned circuit for its collector load has high gain.
A transistor with a resistor for its collector load has low gain at 100MHz.
you will find it easy to make inductors(especially air cored ones) rather than purchasing. just have a look at few. micro and nano henries could well be wound on a meg ohm resistor and used.
ther are simple electronic calculators to guide you for the turns etc,
I you have a faulty night lamp transformer or any poer tansformer, that is faulty, RIP it and you have plenty of wire on secondary to suite your needs.
Or goto a local coil winder and seek few (say 2 or 3) metres of recovered enemelled copper wire ( the enemel is not removed) --
take drill bilt of wanted Dia and wind the ire manually and pull out the drill bit .. your coil is ready-- scap the enamel at the edges and tinker the ends for good soldering..
please go ahead-- why purchase?
The gain of a transistor is determined by the ratio of its collector load impedance to its emitter resistance. At 100MHz the antenna is about 50 ohms to 75 ohms and is in parallel with the collector resistance so the voltage gain is fairly low.
When a tuned circuit is used as the collector load then the voltage gain is higher.
Harry has many FM transmitter circuits on his site. This one uses a PNP RF amplifier transistor with a collector resistor. Other transmitters use an NPN transistor and operate the same. He says the power gain is 10dB which is 10 times the power, but the oscillator's coil is tapped so its output power is low anyway.
with that rf amp posted by audioguru how do you know it's working and what does the variable capacitor do change frequency or what?
how far is the range if you know?
with that rf amp posted by audioguru how do you know it's working and what does the variable capacitor do change frequency or what?
how far is the range if you know?
it is for tuing the paralle tuned LC combination so that only wanted fundametal frequecies are sent to arial and harmonics are suppressed, thus you have to peak it using your Rx as a sensor to get best distance, indirectly indicating that the coil and cap are properly tuned.
I just noticed that your flea-powered kit transmitter operates from only a single 1.0V to 1.5V battery cell!
So I have modified my RF amplifier to work on such a low voltage.
The RF amplifier might not make any difference or it might extend the range to twice as far.
I just noticed that your flea-powered kit transmitter operates from only a single 1.0V to 1.5V battery cell!
So I have modified my RF amplifier to work on such a low voltage.
The RF amplifier might not make any difference or it might extend the range to twice as far.
Well, I've seen some shematic(s) of the wireless microphone(s) on the internet. In these schematics, at the oscillator stage there's a capacitor 33pf(C6) or 47pf(C4) which is connected parallel with the resistor at Transistor's emitor's, I hope you could all see the schematics... well I don't know what do these capacitors do or take effects in these circuits ? Could anyone help me answering this question ?
Thank you all for answering this question
I have 4.5Volts to play with and a power budget of 50mA. How could I make this TX as powerful as possible? I'm using it in the middle of the desert in Australia, so interference is just NOT an issue, I would not do such a thing in suburbia.
Also, TX Freq is set by LC values etc I see, and it will drift with temp, is there any way I could 'easily' incorporate a XTAL or other 'simple' circuit to make it more stable? - stbility is not a big issue, but if it can be increased easily then why not.
What would the actual transmitted power be at TX frequency? in mW if possible.. how would I look at the circuit and calculate this? I am RF electronics trade qualified, just been out of the game for years. appreciate a refresher.
Generally.. wondering how something like this would go against the micromitter chip( Micromitter prject URL ).. in terms of power budget, RF out and stability. The Micromitter does look quite compelling.
which of the many lousy FM transmitters in this thread is the "flea powered " one? The one with the obsolete BA1404 IC?
A few questions please..
I have 4.5Volts to play with and a power budget of 50mA. How could I make this TX as powerful as possible? I'm using it in the middle of the desert in Australia, so interference is just NOT an issue, I would not do such a thing in suburbia.
Look at its datasheet to see its allowed range of supply voltages.
2) Also, TX Freq is set by LC values etc I see, and it will drift with temp, is there any way I could 'easily' incorporate a XTAL or other 'simple' circuit to make it more stable?
No.
It is simple and cheap. its frequency also changes as the battery voltage runs down and if something moves toward the circuit or moves away.
3)What would the actual transmitted power be at TX frequency? in mW if possible.. how would I look at the circuit and calculate this? I am RF electronics trade qualified, just been out of the game for years. appreciate a refresher.
4)Generally.. wondering how something like this would go against the micromitter chip( Micromitter prject URL ).. in terms of power budget, RF out and stability. The Micromitter does look quite compelling.